Antenna system and method for manufacturing the same

ABSTRACT

According to an aspect of the present invention, an antenna system comprises: an antenna panel ( 1 ) which has fine irregularities ( 4 ) on front and back surfaces thereof, the fine irregularities ( 4 ) being formed by blasting so as to regularly reflect service radio waves having longer wavelength than sunlight and scatter sunlight. Further, according to another aspect of the present invention, a method for manufacturing an antenna system in which an antenna panel ( 1 ) is manufactured by combining a plurality of constituent parts, comprises the steps of: finishing front and back surface portions of each of the constituent parts so as to thin down the thickness of constituent parts; blasting the front and back surface portions of the constituent parts with abrasive grains; combining the plurality of constituent parts subjected to the blasting step so as to form the antenna panel ( 1 ) into a desired shape; and attaching an assistant reflecting mirror ( 3 ) to the antenna panel ( 1 ) acting as a main reflecting mirror.

BACKGROUND OF THE INVENTION

The present invention relates to a millimeter-wave antenna system inwhich the influence of sunlight collected near a focal point of anantenna is reduced, and relates to a method for manufacturing such anantenna system.

As such a millimeter-wave antenna system, hitherto there is an antennasystem which has a configuration shown in FIG. 10. FIG 10 is a schematicview of such a background-art antenna system. In FIG. 10, the referencenumeral 1 represents an antenna panel; 2, a coating film painted inwhite or with a semi-gloss on the front surface of the antenna panel 1;and 3, an assistant reflecting mirror disposed on the coating film 2side. Incident millimeter waves are focused on the assistant reflectingmirror 3 by the antenna panel 1. On the other hand, incident light whichis shorter in wavelength than the millimeter waves (not longer than 1μm) is not focused on the assistant reflecting mirror 3 because theincident light is irregularly reflected by the front surface of thecoating film 2. However, if the frequency used in such an antenna systemis higher, there is a problem that the millimeter waves passing throughthe inside of the coating film 2 are attenuated so that the antennasensitivity is lowered or the observed signals to noise ratiodeteriorates.

In order to solve such a problem, in the background art, for example,there is an antenna system disclosed in JP-A-62-131611. FIG. 11 is aschematic sectional view of the background-art millimeter-wave antennasystem. In FIG. 11, fine irregularities 4 are formed on one of thesurfaces of an antenna panel 1. In this background-art antenna system,the antenna panel 1 which has a diameter of about 50 cm and which can beused without painting is manufactured in the following method. That is,very small grooves are formed in the front surface of a flat plate, andthe flat plate is bent and deformed to form the antenna panel 1. Thus,the coating film 2 is eliminated so that the antenna panel 1 can be usedeven in a high frequency. Further, the fine irregularities 4 areprovided on the front surface of the antenna panel 1 so as to restrainlight, which is reflected by the antenna panel 1, from being collectedon a light collecting portion. Thus, the temperature of the lightcollecting portion is prevented from rising.

Thus, the aforementioned fine irregularities 4 in the background-artantenna system are formed by scratching, blasting or etching the frontsurface of the antenna panel 1. Aluminum plates which were 2 mm thickand which were polished on their front surfaces were used for measuringtheir light reflecting properties. FIG. 12 is an explanatory view forexplaining the measuring method.

In the measuring method, as shown in FIG. 12, a flat-plate sample wasmade just opposite to the sun, and measured with an illuminometerprovided with a cylinder so as to detect light only from the front,while the angle of the illuminometer with respect to the flat platesample was changed. FIGS. 13 and 14 are graphs of the reflectingproperties, respectively, of a #40 polished product and a #320 polishedproduct. The RMS (Root Mean Square) front-surface roughness of the #40polished product was 4.4 μm, and that of the #320 polished product was0.7 μm. Incidentally, #40 and #320 designate the granularities (sizes)of abrasive grains respectively. The abrasive grain size becomes smalleras the number is larger. FIGS. 13 and 14 show that the illuminance wasvery high near the angle of 0° in each product, and light was notscattered so much. However, because it is assumed in the background-artantenna system that the diameter of the antenna panel is about 50 cm, alittle effect can be generated even by such reflecting properties.

Theoretically, to what extent the reflecting properties are required isdetermined as follows. FIG. 15 is a relationship graph showing therelationship between the ratio of scattered light collected on anassistant reflecting mirror (450 mm) which is in a focus portion and thescatter angle (half width.), in the case of a large-size millimeter-waveparabolic antenna system which is of the order of 10 m. In this case,the energy entering a parabolic antenna is 1×10⁵ W when the parabolicantenna is just opposite to the sun. When this energy is multiplied bythe light collecting ratio and the absorptivity of the assistantreflecting mirror, the temperature rises by about 100° C. if the lightcollecting ratio is 0.015. Such temperature rising is considered to bethe limit in use if the time for the parabolic antenna to be justopposite to the sun is not so long. On the other hand, the scatteringangle is 55 degrees when the light collecting ratio is 0.015.Accordingly, the scattering angle has to be larger than the above value55 degrees. The scattering angle was 10 degrees in the aforementionedsamples which were mechanically polished. According to similarcalculation, the temperature rises up to 2,000° C. when the lightcollecting ratio is 0.3. Since this temperature exceeds the meltingpoint of aluminum (Al), the samples are not applicable.

In addition, in order to use also in high frequency, the RMSfront-surface roughness has to be not larger than 10 μm all over theantenna panel which is of the order of 10 m. Therefore, when the antennapanel is finished, the warp (distortion) of the antenna panel has to besuppressed as small as possible. Even if a good mirror surface accuracyof the antenna panel can be obtained by machining before polishing,there may be a case that a predetermined mirror surface accuracy cannotbe obtained after the front surface of the antenna panel is polished.Further, when a very high-precision antenna panel aimed at millimeterwaves and submillimeter waves is manufactured and in order to finish thefront surface of the antenna panel into a mirror surface with less“swell” by machining or the like, it is difficult to groove the mirrorsurface beforehand. In addition, it is very difficult to polish thecurved surface of the antenna panel after the antenna panel is formed tohave a mirror surface.

SUMMARY OF THE INVENTION

Therefore, the present invention was developed to solve the foregoingproblems. It is an object of the present invention to provide a novelantenna system in which fine irregularities are formed on the front andback surfaces of an antenna panel by blasting so that the warp of theantenna panel can be reduced to ensure the front surface accuracy of theantenna panel while sunlight can be restrained from being collected; andto provide a method for manufacturing such an antenna system.

According to an aspect of the present invention, as stated in Aspect 1,an antenna system comprises an antenna panel which has fineirregularities on front and back surfaces thereof, the fineirregularities being formed by blasting so as to regularly reflectservice radio waves having longer wavelength than sunlight and scattersunlight.

Preferably, as stated in Aspect 2, in the antenna system according toAspect 1, a chemical surface film is formed on the front surface of theantenna panel where the fine irregularities have been formed.

Preferably, as stated in Aspect 3, in the antenna system according toAspect 1 or 2, the fine irregularities are in a range of from 0.1 μm to1.0 μm in RMS front-surface roughness.

Preferably, as stated in Aspect 4, in the antenna system according toAspect 2 or 3, the chemical surface film is formed by alodineprocessing.

Preferably, as stated in Aspect 5, in the antenna system according toAspect 1 to 4, the chemical surface film is colorless.

According to another aspect of the present invention, as stated inAspect 6, a method for manufacturing an antenna system in which anantenna panel is manufactured by combining a plurality of constituentparts, comprises the steps of: finishing front and back surface portionsof each of the constituent parts so as to thin down the constituentparts; blasting the front and back surface portions of the constituentparts with abrasive grains after the finishing step so as to form fineirregularities on front and back surfaces of the antenna panel;combining the plurality of constituent parts subjected to the blastingstep so as to form the antenna panel into a desired shape; and attachingan assistant reflecting mirror to the antenna panel acting as a mainreflecting mirror.

Preferably, as stated in Aspect 7, the method according to Aspect 6further comprises the step of applying surface treatment to theconstituent parts subjected to the blasting step.

Preferably, as stated in Aspect 8, in the method according to Aspect 7,the surface treatment step is performed by application of alkali washingor acid washing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematically enlarged sectional view of the front surfaceof an antenna panel in an antenna system according to the presentinvention.

FIG. 2 is a characteristic graph showing the relationship between RMSfront-surface roughness and service frequency of the antenna panelaccording to the present invention.

FIG. 3 is a characteristic graph of energy with respect to thewavelength of the antenna panel according to the present invention.

FIG. 4 is a sunlight reflecting characteristic graph in the case whereblasting was performed on the front surface of the antenna panelaccording to the present invention.

FIG. 5 is a characteristic graph showing the relationship between thegranularity of alumina abrasive grains and RMS front-surface roughnesson the antenna panel according to the present invention.

FIG. 6 is a characteristic graph of the antenna panel according to thepresent invention with respect to blast pressure.

FIG. 7 is a schematic view of measuring equipment for measuring thesituation of temperature rising of a sample according to the presentinvention.

FIG. 8 is a temperature rising characteristic graph in the case whereonly processing of blasting was performed on a sample of an antennapanel according to the present invention.

FIG. 9 is a temperature rising characteristic graph in the case whereprocessing of alkali washing was further performed on the antenna panelaccording to the present invention.

FIG. 10 is a schematic view of a background-art antenna system.

FIG. 11 is a typical sectional view of a background-art millimeter-waveantenna system.

FIG. 12 is an explanatory view for explaining a method of measuringreflecting properties of the background-art antenna system.

FIG. 13 is a reflecting characteristic graph of one background-artantenna system.

FIG. 14 is a reflecting characteristic graph of another background-artantenna system.

FIG. 15 is a relationship graph showing the relationship between theratio of scattered light collected on an assistant reflecting mirrordisposed in a focus portion of a background-art large-sizemillimeter-wave parabolic antenna system and the scattering angle (halfwidth).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Embodiment 1)

Embodiment 1 of the present invention will be described with referenceto FIG. 1. FIG. 1 is a sectional view showing the front surface of anantenna panel 1 enlarged schematically. The antenna panel 1 is made ofan aluminum alloy, and fine irregularities 4 are formed in the front andback surface portions of the antenna panel 1. As shown in FIG. 1, theantenna panel 1 is configured so that incident sunlight is irregularlyreflected by the formation of the fine irregularities 4 in the frontsurface portion of the antenna panel 1 while service radio waves whichare longer in wavelength than the sunlight are reflected regularly. Thefine irregularities 4 are formed by blasting in which alumina abrasivegrains (#400) are blasted on the front and back surface portions of theantenna panel 1 at a predetermined blast pressure, for example, about0.2 MPa (Pa is a unit of pressure). The reason why blasting is performedon the front and back surface portions of the antenna panel 1 is thatblasting prevents a warp of the antenna panel 1 from generating. Sinceblasting is performed by blasting abrasive grains onto the front surfaceof the antenna panel 1 to be finished, the fine irregularities 4 can beformed substantially uniformly all over the front surface of the antennapanel 1 no matter how curved the surface is.

(Embodiment 2)

Next, description will be made about a method for manufacturing anantenna panel according to Embodiment 1 of the present invention. Theantenna panel 1 is constituted by combining a plurality of constituentparts. The respective constituent parts are made of an aluminum alloy,and set to be about 1 m square and about 30 mm thick. Each of theconstituent parts has a predetermined radius of curvature in accordancewith its own position in the antenna panel 1 so as to form a 10 m-orderantenna panel. Each of the constituent parts is too heavy in weight ifit is used as it is. Therefore, each of the constituent parts is thinnedby machining its front and back surfaces by a machining center so as tobe formed to be 2 to 3 mm thick. At this time, the front surface of theantenna panel 1 is restricted to be not larger than 10 μm in RMS. Then,alumina abrasive grains (#400) are blasted all over the back surface ofeach of the constituent parts as described above. At this time, theblast pressure of the alumina abrasive grains is set to be about 0.2MPa. Similarly, alumina abrasive grains are blasted all over the frontsurface of each of the constituent parts. By blasting the front and backsurfaces of each of the constituent parts thus, a warp which might beproduced by blasting only the front surface is reduced.

For example, in an aluminum alloy plate which is 100 mm square and 2 mmthick, a warp of about 200 μm is produced if blasting is performed ononly the front surface of each constituent part, while the warp can bereduced to be about 3 μm or less if blasting is performed on both thefront and back surfaces. With this curvature, a warp exceeds 10 μm whenthe aluminum alloy plate is 1 m square. However, the antenna panel 1 isabout 2 to 3 mm thick, that is, a little thicker than the aluminum alloyplate. Accordingly, there is no fear that the warp (distortion) due toblasting exceeds a predetermined value. Then, alodine processing isgiven to the respective constituent parts after blasting has beencarried out on these parts, and the constituent parts are combined withone another in their predetermined positions. Thus, the front surfaceaccuracy of the panel can be made not larger than about 10 μm in RMSfront-surface roughness. Thus, the antenna panel 1 having a desiredshape is constituted by a combination of the plurality of constituentparts. The assistant reflecting mirror 3 is attached to the antennapanel 1 acting as a main mirror so as to form a Large-size antennasystem which is for the order of 10 μm.

Further, Embodiment 2 of the present invention will be described withreference to FIG. 2. FIG. 2 is a characteristic graph showing therelationship between the RMS front-surface roughness on the antennapanel 1 and the service frequency of the antenna panel 1. As shown inFIG. 2, in order to make the service frequency available up to a highfrequency of about 10 THz, it is necessary to make the antenna panel 1not larger than 1 μm in RMS front-surface roughness. On the other hand,theoretically, light scattering is expressed by the equation (regularreflected light)/(total reflected light)=exp[−(4π Rrms/λ)2] if theincident angle is a right angle. That is, Rrms of about half awavelength is required. In addition, as shown in FIG. 3, sunlight hasthe largest energy (J/m3s) at a wavelength (λ) in a range of from 0.4 μmto 0.6 μm. Accordingly, if the front surface roughness is not smallerthan 0.1 μm which is ¼ of the wavelength, the regular reflectedcomponent becomes 1% or less of the total reflected light. Therefore,taking the light scattering and the service frequency intoconsideration, the front surface roughness is in a range of from 0.1 μmto 1 μm in RMS front-surface roughness.

Next, FIG. 4 is a sunlight reflection characteristic graph in the casewhere the front surface of an antenna panel is subjected to theaforementioned blasting. In this case, the RMS front-surface roughnessis about 0.34 μm, and the half width (the width having half a peakvalue) is larger than 55° so that sunlight is considerably scattered onthe front surface of the antenna panel. By scattering the sunlight thus,it is possible to restrain the assistant reflecting mirror 3 from risingin temperature.

Although the #400 alumina abrasive grains were used in the abovedescription, abrasive grains are not limited thereto. Alumina abrasivegrains other than #400 maybe used, or abrasive grains of ceramics,resin, or metal other than alumina may be used. FIG. 5 is a granularitycharacteristic graph showing the relationship between granularity of the#400 alumina abrasive grains and RMS front-surface roughness on theantenna panel. As shown in FIG. 5, the larger the abrasive grain size,the larger the RMS front-surface roughness. On the other hand, FIG. 6 isa characteristic graph of the RMS front-surface roughness with respectto blast pressure (MPa) of the #400 alumina abrasive grains. The blastpressure is not limited to the above-mentioned value 0.2 MPa. Further,there is a tendency that the warp of the antenna panel grows up as thefront surface roughness thereof increases. However, if blasting isperformed on the front and back surfaces of the antenna panel asdescribed above, the warp can be reduced considerably. Accordingly, theblast pressure and the abrasive grain size can be established withreference to FIGS. 5 and 6 so that the fine irregularities 4 formed onthe front surface of the antenna panel have RMS front-surface roughnessin a range of from 0.1 μm to 1.0 μm. Further, blasting may be performedon each of the front and back surfaces of the antenna panel only once ora plurality of times.

The processing steps after the above-mentioned blasting are as follows.That is, an alkaline degreasing step, a light etching step by alkali(NaOH) washing, a desmutting step, and an alodine processing step areperformed sequentially. Incidentally, water washing and so on areincluded in each step. If the chemical surface film 5 formed on thefront surface of the antenna panel were colored for some reason, thesunlight absorptivity would increase so that the temperature of theantenna panel would increase. As a result, the antenna panel mightdeteriorate in accuracy and properties. It is therefore preferable thatthe chemical surface film 5 is colorless.

According to Embodiments 1 and 2 described above, millimeter wavesentering the antenna panel 1 are reflected without scattering whilekeeping the incident angle. On the other hand, incident sunlight isirregularly scattered on the front surface of the antenna panel 1without being collected, so that the assistant reflecting mirror 3 orstays are not affected by the reflected sunlight. In addition, becausethe chemical surface film 5 is provided by alodine processing on thefront surface of the antenna panel 1, the antenna panel 1 can be formedto be rich in weatherability.

(Embodiment 3)

In Embodiment 3 of the present invention, blasting is performed on thefront and back surfaces of an antenna panel 1 so as to provide fineirregularities 4 in the front and back surfaces in the same manner as inEmbodiment 1 or 2. After the blasting is performed on the antenna panel1, the antenna panel 1 is not subjected to such chemical surface filmtreatment as shown in Embodiment 1, but the antenna panel 1 is assembledafter alkali washing or acid washing is performed. The aluminum frontsurface of the antenna panel 1 has to be covered with the chemicalsurface film 5 in the case where the antenna panel 1 is disposedoutdoors to be exposed to the weather. However, there may be a case thatthe chemical surface film 5 need not be provided if the antenna panel 1is disposed in a location where it rarely rains or there is little saltdamage. In such a case, it will go well if alkali washing or the like isperformed after blasting. On the other hand, if blasting were performedonly on the front surface of the antenna panel 1, plastically deformedaluminum which is a raw material of the antenna panel 1 would get darkto absorb a part of sunlight without irregularly reflecting it. As aresult, the temperature of the antenna panel 1 itself would rise tolower the antenna measurement accuracy. Therefore, alkali washing or thelike is performed on the front surface of the antenna panel 1 so as toetch the front surface layer thereof slightly and eliminate dust and soon. Thus, the front surface of the antenna panel 1 becomes whitishenough to restrain the antenna panel 1 itself from rising intemperature.

Here, FIG. 7 is a schematic view of measuring equipment for measuringthe situation of temperature rising of a sample 6. The sample 6 was analuminum plate which was 200 mm square and 2 mm thick. A thermocouple 7was attached to the back surface of the sample 6, and the back surfaceof the sample 6 was pasted on expanded polystyrene 8. The sample 6 wasdisposed so that the front surface thereof was substantiallyperpendicular to incident sunlight to thereby measure the temperaturerising. Incidentally, because this measuring method was greatly affectedby the wind or the weather at the time of measuring, a comparativesample (not shown) had to be set. FIGS. 8 and 9 are temperature risingcharacteristic graphs in the case where only processing of blasting wasperformed on the sample 6 and in the case where processing of alkaliwashing was further performed on the sample 6 after the blasting,respectively. It is understood from FIG. 8 that the temperature risingin the case where blasting was performed was larger than in the case ofwhite painting or #150 polishing. It is also understood from FIG. 9 thatthe temperature rising in the case where alkali washing was furtherperformed could be restrained to the same level as that in the case ofwhite painting. Although alkali washing was adopted here, any otherwashing method or light etching may be adopted so long as it has aneffect of removing dust, degeneration due to processing, or the like,adhering to the front surface of the sample 6.

According to an antenna system of the present invention, fineirregularities are formed on the front and back surfaces of an antennapanel by blasting so that the warp of the antenna panel can be reducedto ensure the front surface accuracy of the antenna panel while sunlightcan be restrained effectively from being collected.

In addition, according to a method for manufacturing the antenna systemaccording to the present invention, an antenna panel is manufactured bycombining a plurality of constituent parts. The plurality of constituentparts are subjected to blasting so that fine irregularities are formedon the front and back surface portions of the respective constituentparts. The plurality of constituent parts subjected to blasting thus arecombined to form an antenna panel having a desired shape. It istherefore possible to manufacture a high-precision large-size antennasystem.

What is claimed is:
 1. An antenna system comprising: an antenna panelwhich has fine irregularities on front and back surfaces thereof, saidfine irregularities being formed by blasting so as to regularly reflectservice radio waves having longer wavelength than sunlight and scattersunlight.
 2. The antenna system according to claim 1, wherein a chemicalsurface film is formed on said front surface of said antenna panel wheresaid fine irregularities have been formed.
 3. The antenna systemaccording to claim 2, wherein said chemical surface film is formed byalodine processing.
 4. The antenna system according to claim 2, whereinsaid chemical surface film is colorless.
 5. The antenna system accordingto claim 1, wherein said fine irregularities are in a range of from 0.1μm to 1.0 μm in RMS front-surface roughness.
 6. A method formanufacturing an antenna system in which an antenna panel ismanufactured by combining a plurality of constituent parts, comprisingthe steps of: finishing front and back surfaces of each of saidconstituent parts so as to thin down said constituent parts; blastingsaid front and back surfaces of said constituent parts with abrasivegrains after said finishing step so as to form fine irregularities onfront and back surfaces of said antenna panel; combining said pluralityof constituent parts subjected to said blasting step so as to form saidantenna panel into a desired shape; and attaching an assistantreflecting mirror to said antenna panel acting as a main reflectingmirror.
 7. The method for manufacturing an antenna system according toclaim 6, further comprising the step of: applying surface treatment tosaid constituent parts subjected to said blasting step.
 8. The methodfor manufacturing an antenna system according to claim 7, wherein saidsurface treatment step is performed by application of alkali washing oracid washing.